Double clutch transmissions for motor vehicles are known in the art. Their principal advantage over conventional stepped manual transmissions is that the shifting processes of a gear change take place almost without interruption in propulsive force. In this manner, frequent changes in acceleration and load during gear shifting are avoided, resulting in more comfortable handling and enabling a sportier driving mode. In a popular construction, described in DE 101 34 118 A1, the double clutch transmission is equipped with two drive shafts (transmission input shafts), which are arranged co-axially in relation to one another, each with a friction clutch assigned on the input side, and a transmission wheel set for a group of gears, preferably with even-numbered gears on one side and odd-numbered gears and a reverse gear on the other side, assigned on the transmission side. The one drive shaft is configured as an external hollow shaft, inside of which the other drive shaft is disposed as an internal, central shaft, whereby the internal shaft emerges from the external shaft in a transition area inside a transmission chamber. Power is transmitted alternatingly via one of the drive shafts at a time.
A gear change is implemented via an overlapping release and engagement of the two clutches whereby, in each case, two gears are engaged sequentially to the drive shafts. Transmissions of this type are most frequently configured as automatic transmissions, i.e., the selected gear changes are controlled via hydraulic/electric actuators. Wet multi-plate clutches are usually used as the friction clutches and are situated in a clutch chamber adjacent to a transmission chamber, which accommodates the transmission wheel set for the double clutch transmission.
The clutch chamber and the transmission chamber can form a shared oil chamber inside the transmission housing. In contrast, an oil chamber divider, such as is described in DE 35 30 017 A1 and in DE 41 15 989 A1, offers the advantage of being able to use different oils for the double clutch and for the transmission with each oil being specially adapted to its specific requirements. In this case, the two oil chambers must be sealed off from one another, to prevent the oils from mixing together. In principle, in sealing oil chambers for transmissions, the technique of sealing shaft passages with radial shaft sealing rings is known. Sealing rings of this type generally have a U-shaped profile, on one leg of which a sealing lip is formed, which rests against the corresponding shaft. However, double clutch transmissions have the problem that the oil chambers must also be sealed off from one another directly in the area in which the radially interior drive shaft emerges from the radially exterior drive shaft inside the transmission chamber, because the two oil chambers are connected to one another via an annular gap between the shafts.
From DE 10 2004 046 297 A1, which was previously undisclosed, an arrangement for sealing co-axial drive shafts is known in which an enlarged annular gap is provided in the area in which the inner central shaft emerges from the outer hollow shaft. A double sealing ring, comprised of two radial shaft sealing rings, is positioned in the annular gap at the end. The double sealing ring rests in the hollow, exterior drive shaft and forms a seal against the interior drive shaft with the sealing lips of the two radial shaft sealing rings. Between the two radial shaft sealing rings, an intermediate space is provided, which is connected to a drain for ventilation and for leakage detection. The known configuration provides a structurally simple seal of the two shafts.
The disadvantage of this configuration is that the radial shaft sealing rings are acted upon by rotational speed as the exterior hollow shaft rotates. The resulting centrifugal forces can cause the sealing lips to separate from the central drive shaft, thereby impairing the seal tightness of the configuration. In addition, the drain used for ventilation and aeration, as well as for leak detection, is a relatively complicated structurally.
In consideration of the above, the object of the invention is to provide a sealing device of the type initially described, which will ensure a more reliable seal of two co-axial drive shafts, with one shift being partially accommodated inside the other, and which will simultaneously offer a simple option for ventilation and leakage detection.